Patent GB-870343-A (GB)
Title: Improvements in or relating to electron discharge devices
Inventor: MCGEE JAMES DWYER
IPC: H01J31/50
Filed: 1958-07-02
Abstract: 870,343. Discharge apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 22, 1959 [July 2, 1958], No. 21154/58. Class 39(1). A method of manufacturing an image intensifier tube having at least two stages involves constructing a device having a metallic layer 'firststage' photo-cathode 35, Fig. 1, on mica window 6 and a second stage fluorescent screen comprising phosphor layer 33 on similar mica window 10, the two layers being disposed at each end of a tubular envelope 2 which has side tube 11 having entry 12 into envelope near the input end of the device, and which envelope contains a slide tube 13 which may move from the position shown to the position indicated in outline at 13<SP>1</SP> adjacent to the input end of the device. Accelerating electrodes 27 of the first stage of the device are in the slide tube, and these have contacts external to the slide tube which engage spring contacts 24 when the slide tube is in position 13<SP>1</SP>, the accelerating electrodes 21 of the second stage of the device being disposed on the walls of the envelope 2 between the end 31 of the slide tube of fluorescent screen 33. A multiple layer plate is built up on mica plate 32 with a fluorescent layer 34 and layer of antimony backed by aluminium film 36. When the slide tube in position 13 (i.e. as shown), the device is degassed and caesium vapour is introduced into the space 38 of the device and the antimony layers 35, 36 are activated by the vapour. The vapour does not enter other parts of the device as the multiple layer screen 32, forms an air-tight seal on flange 30 of tube 13. Absorbing means and pumping out of tube through side-tube 11 remove the excess Cs. vapour. The side. tube is then sealed off. The multiple layer screen 32 is then turned about-face so that the fluorescent layer 34 faces the photo-cathode 35, is moved so that it abuts against the flange 31 of slide tube 13 where it is held in place by spring loaded clips. The slidetube is then moved to position 13<SP>1</SP> and held in position by spring clip 17 20 in bulge 18 of the envelope, the pointed end of the clip 20 engaging a suitable indentation in the slide tube 13. In the degassing operation a magnetic chock 39, Fig. 2, is inserted over the flange 30 so that a gap exists around the periphery of the un-activated multiple layer screen 32. When the out-gassing is completed a magnet is used to dislodge the chock which is then shaken about in the space 38 until it drops through the outlet tube 11. The unvelope comprises a main tubular portion of glass 2 and metal extensions 3, 7 at each end. To the end 3 sealing flanges 4, 5 are provided and between these is sealed in an air-tight manner, a mica window, one thousandth of an inch thick. The construction of the other end of the device is the game. When the interior of the device is evacuated the mica windows bow inwardly as a result of atmospheric pressure, and distortion of the light input is counteracted by the use of a light guide 37, which comprises a number of fibres and utilises the property of total internal reflection. The light guide has a suitable convex end to engage accurately with the concavity of the mica window. The slide tube is provided with rings 14, 15 on which it may slide.